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Polishing Compound In Relation To Grit Size?

If black & green polishing compound had a grit size what would it be? I've seen some videos where people sharpen their knives through a multitude of stones and then through a multitude of strops with different compounds. Now if the black compound has a "grit value" of the same as the first stone he used, wouldn't that be like starting over? So my question is, how much grits does green and black compound have? I know they are measure in microns or something but I don't understand that. Any help?

Some polishing compounds use friable abrasive. This means that as you use the abrasive, it breaks down into smaller and smaller particles. I could be wrong, but I think Flitz and/or Simichrome use friable aluminum oxide? If so, that makes it really difficult to determining the grit of the polish. Not all polishes are friable, though, so for non-friable polishes, it may be easier (although often still unclear) how to estimate a grit size.

The whole question of what is grit size, turns out to be surprisingly complicated. First of all, any compound or abrasive has a range (histogram/distribution) of grain sizes, so a single number cannot accurately characterize it. Typically, all that is posted is the d50 number, which is the median grain size where the median is calculated with respect to the total weight (ie: half of the weight of the sample is made up of particles smaller than X, the other half of the weight of the sample is made up of particles larger than X). Next, a lot of other effects could be in play: the shape of the particles (round and smooth, or sharp and blocky), whether or not the abrasive if friable (breaks down into smaller particlse), and hardness and type of abrasive (diamond, or SiC, or aluminum oxide...).

So far I haven't seen a complete solution to the huge variation of what a grit number "means". The best I've seen is Komitadjie's Grand Unified Grit Chart. Short of that, the other thing is experience; various people saying,"In my experience, compound A from company B seems similar to a grit number of C for company D." I wish it weren't so complicated.

Another thought to consider - the use of an abrasive on a backing with any amount of give to it will dramatically reduce the "effective" grit value. I did a few tests using the abrasive taken from a waterstone to finish the ground edge off the same stone. I applied it to some newspaper and used it as a strop - the scratch pattern was a fraction of what the same abrasive produced while embedded in a solid binder.

I have some 600 grit silicon carbide powder that, when applied to firm leather, can improve the scratch pattern following 1200 grit sandpaper.

There's a multitude of variables when it comes to stropping, any change to the density of the backing, how much metal swarf is mixed with the compound over time, the abrasive breaking down, small changes in pressure and angle....

As mentioned, there's a huge variety in what's known as 'black' or 'white' compounds, in particular. Very wide range of grit sizes for each, and at least with 'white' compounds, many aren't even of the same abrasive type. Many are aluminum oxide, some might even be talc (softest material on the Moh's scale). There's even a compound known as 'white diamond', which has no diamond and no aluminum oxide. It's tin oxide. Most 'green' compound is comprised of chromium oxide at pretty small grit size (at least less than 1 micron, with many averaging ~0.5 micron). Some 'green' chromium oxide compounds are mixed with other abrasives, like aluminum oxide.

Silicon carbide (black) is friable, so it fractures into smaller, but still very sharp and aggressive particles. Some, but not all aluminum oxide is friable. Individual processes used to create the stuff will make big differences in how each behaves. I don't know whether Flitz/Simichrome uses friable AlOx, but I hope they do (at that level of polish, that just means it gets even better). The aluminum oxide used in Spyderco's ceramics is of the same fixed grit size, even across all of their ceramic 'grit' specs. Their finishing process is what makes the 'effective grit' different for each. The abrasive itself doesn't change or break down with use.

The substrate (backing) used with the compound is a huge variable. One can take a single compound of fixed type and size, and apply it to soft, thick leather (less aggressive), firm or thin leather (more aggressive), balsa wood (even more aggressive), and then on hardwood (more, more, more so). Look at the 'black stuff' (metal) removed from the blade and left on the strop in each case, and you can easily see the difference in performance. Sort of like comparing the feeling of pebbles under your bare feet, if you walk on them on thick, deep carpet, or on bare concrete. One way is going to dig a lot deeper and hurt a lot more, depending on the 'cushion' underneath.

Long story short, the only consistent way to know a particular compound is to try it out, and see how it performs. It does help greatly to know the exact type and size of the abrasive starting out, but many manufacturers don't specify such details. And many dealers/vendors may not even know.

For just starting out, you might try just some Simichrome or Flitz, or the reputable diamond compounds (DMT, Hand American) are much more consistent and predictable, too. I like Simichrome, and often use it on one of my strops. I don't doubt Flitz is also good; many here seem to like it also. So many of the generic bar/stick compounds are just too unpredictable, until you've actually used them for a while, and can figure out where they 'fit' in a stropping/polishing sequence.

If you want stropping compounds of a known size, you might also check out some of these at chefknivestogo.com that have micron ratings. These probably also polish given how fine they are, but I haven't had a lot of experience with them. I own some of Ken Schwartz's CBN, but have not yet had a chance to really test it (Ken's stuff is strongly recommended in knifeforums.com). A lot of people here really like Hand American's green chromium oxide semi-paste, and also the boron carbide semi-paste.http://www.chefknivestogo.com/handamerican.htmlhttp://www.chefknivestogo.com/kenscorner.html

Flitz and Simichrome are also popular polishes.

Sincerely,
--Lagrangian

P.S. For reference: Visible light has a wavelength of 0.4 to 0.7 microns. So if your scratches start getting smaller than about 0.2 microns, you are into the optically smooth realm. Probably a an abrasive particle will make a scratch much smaller than it's diameter, especially if it is on a soft surface like strop. Prof. Verhoeven looked at modern razor blades, and found that they are sharp to about 0.4 microns as well. This may give you some guidance on grits for polishing. For coarser grits, you might check out Komitadjie's Grand Unified Grit Chart which is a sticky in this forum.

Last edited by Lagrangian; 05-23-2012 at 07:23 PM.
Reason: Clarified some points in the P.S.

can someone direct me to some diamond paste. i can seem to find it online. does it look like a polishing bar or does this come in a tube or can?

I use DMT Dia-Paste. It comes in small tubes (syringes, actually; very convenient applicator). Looks like a very small quantity, but a tiny dab of this stuff will last a very long time, on a strop. Comes in 6/3/1 micron sizes. Each can be purchased individually, but here's an 'all-in-one' assortment from knifecenter (BF member dealer):

so is diamond paste recommended for strop to use on convex edges? ill be mostly sharpening convex knives. thats a great deal. do these last a long time? and do i have to apply a bunch like you do with polishing compounds bars?

so is diamond paste recommended for strop to use on convex edges? ill be mostly sharpening convex knives. thats a great deal. do these last a long time? and do i have to apply a bunch like you do with polishing compounds bars?

It'll be fine for convex (or any other edge type). It does last a very long time. I usually apply it in small 'dots' (~1/8" or so); maybe 3 or 4 dots on the smallish strop blocks I use (< 6" length). A flexible plastic ruler is very handy as a spreader, and will help even out the application. If put on too heavy, the surface of the strop will be very sticky/pasty after the compound dries, and any excess compound will simply be scraped off, onto your blade. This is why it's important to apply it very, very sparingly. Don't want to waste any of it. If the application turns out to be a little too light, just add a very tiny bit at a time (maybe one 'dot'), and try it again.

The diamond paste, and Ken Schwartz' CBN / Diamond sprays are both exceptionally good for hand strops on all kinds of edges and metals.

For powered strops, Ken offers a paste version, and Hand American offers a Boron Carbide 1u paste, and a .5u CrO paste that are both excellent. The Hand American stuff works just as well on hand strops as powered, as well.

I already own a nice strop loaded with green compound, but I find it useful only for polishing an a already well sharpened edge. I think I’d like to buy a nice two sided strop loaded with CBN emulsion that would sit above the green strop in coarseness. For comparison purposes, approximately what grit CBN compound would be comparable to the green strop compound and which 2 CBNs would you recommend to sit above that? This is for maintaining sharp hunting knives. They don't need to split hairs.

I already own a nice strop loaded with green compound, but I find it useful only for polishing an a already well sharpened edge. I think I’d like to buy a nice two sided strop loaded with CBN emulsion that would sit above the green strop in coarseness. For comparison purposes, approximately what grit CBN compound would be comparable to the green strop compound and which 2 CBNs would you recommend to sit above that? This is for maintaining sharp hunting knives. They don't need to split hairs.
Thanks.

What steel(s) are these knives made with? Depending on what, you might not need CBN anyway, and it may just be extra expense and over-complicating things; especially if maintaining a relatively toothy edge on hunting knives. Multiple compounds in sequence usually wouldn't be needed unless you're pursuing a mirror finish on your bevels. If you are, that's fine; but you might not need anything that elaborate for a good working edge on a hunting blade. On those, most of the working character of the edge will come directly from the stone, and minimal refinement needed on strops, save for cleaning up loose burrs (assuming the stone work is good in the first place).

All Compounds are really high grit in comparison to any stone. Most of the common compounds are 30k - 60k. We are talking microns here and grit is not the only factor. The hardness of the abrasive and the amount of binder to abrasive you get will make a difference. Most people will finish on a stone that is around 1000 - 2000 grit for pocket knives and around 8000 - 12000 for straight razors. From there you would strop. If you want to go through reach color you would first start with Black, then White, Green, Red, and finish on smooth veg leather.

... you would first start with Black, then White, Green, Red, and finish on smooth veg leather.

Please note that this order of colors is not universally valid.
As Komitadjie wrote already in post #2 in this very thread There are a LOT of compounds, and they're all different.
Every maker has a different formulation, and one maker's "black"
compound is going to be very different from another's.

Two examples: if your compounds were of the Neroli brand,
you would use the colors in this order: Yellow, Green, Grey, Red, Blue, and White.
If you fancy the Luxor brand, the order would be Red, Green, Grey, Blue, Yellow, White, and Orange.

Great fun, eh?

To make things even worse, just because a certain compound is green,
you can't be sure that it contains CrOx. And if it should happen to contain
CrOx, you cannot be certain that it is of the 0.5 Micron variety (ref. Brent Beach).

Unfortunately, most manufacturers consider the contents a trade secret.
In Germany, they just publish relative values of Cut and Gloss on a scale
from 1 to 10. I have found one manufacturer (in France) that publishes
grit size (seven compounds from 6.5 Micron down to 0.1 Micron).
Hopefully, others might do the same in the future.